Conventional approaches for regulated devices implement independent regulators for analog portions (i.e., phase lock loops (PLLs)) and digital portions(i.e., logic core) of a circuit. With independent regulators, switching in the core does not affect the PLL devices. However, providing separate reference voltages requires additional overhead.
It is desirable to provide a circuit to prevent gate oxide breakdown of regulated, thin-oxide devices in a PLL when another device, implemented on the same integrated circuit (IC), is operated when the PLL is powered down.